Inkjet printing mechanisms employ pens having printheads that reciprocate over a media sheet and expel droplets onto the sheet to generate a printed image or pattern. Such mechanisms may be used in a wide variety of applications, including computer printers, plotters, copiers, and facsimile machines. For convenience, the concepts of the invention are discussed in the context of a printer.
A typical printhead includes a silicon-chip substrate having a central-ink aperture that communicates with an ink-filled chamber of the pen when the rear of the substrate is mounted against the cartridge. An array of firing resistors is positioned on the front of the substrate, within a chamber enclosed peripherally by a thin-film layer surrounding the resistors and the ink aperture. An orifice layer connected to the thin-film just above the front surface of the substrate encloses the chamber, and defines a firing chamber just above each resistor. Additional description of basic printhead structure may be found in “The Second-Generation thermal Inkjet Structure” by Ronald Askeland et al. in the Hewlett-Packard Journal, August 1988, pages 28-31; “Development of a High-Resolution Thermal Inkjet Printhead” by William A. Buskirk et al. in the Hewlett-Packard Journal, October 1988, pages 55-61; and “The Third-Generation HP Thermal Inkjet Printhead” by J. Stephen Aden et al. in the Hewlett-Packard Journal, February 1994, pages 41-45.
In order to minimize the number of required printheads for a complete printing system and to obviate the need to align separate printheads in a printing system, it is desirable to have the ability to include firing chambers of different drop weights, for example a color column and a black column, on a single printhead. In the past, manufacturers have been unable to make printheads with firing chambers of different drop weights, because firing chambers of different drop weights traditionally required different orifice-layer thicknesses in order to produce the best ink trajectory and drop shape with optimum energy efficiency.
Accordingly, it is an object of the present invention to provide designs for and methods of manufacturing inkjet printheads with firing chambers capable of printing varying drop-weight quantities of ink with optimal energy efficiency and dot shape.